Liquefied gas storage



Nov. 22, 1949 o. L. GARRETSON LIQUEFIED GAS STORAGE Filed Feb. 18, 1946mVENR.

.1.. GARRETsoN ATTORNEYS low temperature.

Patented Nov. 22, 1949,

` 2,488,813 LIQUEFIED Ges s'ronaon Owen L. Garretson, Bartlesville,Okla., assigner to Phillips Petroleum Company, a corporation of DelawareApplication February 18, 1946, Serial No. 648,497

'z claims. l

This invention relates to the storage of liqueed gases. In one of itsmore speciilc aspects it relates to a method for the storage ofliquefied petroleum gas.

Because of their high vapor pressure at atmospheric temperature,liquefied gases such as hquid propane require high pressure storagevessels or lower pressure vessels thermally insulated and their contentskept cool by some type of ar- Aticial cooling. Large size or largecapacity` refrigeration units are frequently used 1n an attempt tomaintain low pressure storage through Even in large L. P. G. (liqueiiedpetroleum gas) installations such as required by utilities, the amountof refrigeration required for simple storage purposes is not large. Thisfact is yoccasioned by eilicient insulation of the storage tanks.

Maximum refrigeration loads occur at times when tank car or transporttruck quantities of liquefied gas are transferred to the storage tanks.A large quantity of warm liqueed gas may warm the tank and its smallvolume of remaining liquid to such a temperature that the correspondingvapor pressure may be too high for safe storage. The liquid then shouldbe cooled prior to transfer to storage. A refrigeration unit sulcientlylarge to cool a tank car of liquid propane from say 100 F. to a desiredstorage temperature of say F. during a normal unloading period of timewould be greatly oversize for temperature maintenance merely forstorage. Since a refrigeration unit is a type of equipment which isquite expensive it is desirable to use as small a unit as possible. Bythe application of my invention I am able to use a relatively smallrefrigeration unit to serve the two-fold purpose of temperaturemaintenance in storage and cooling during unloading.

For practicingthe process of my invention I use a refrigeration unit ofa size slightly larger than that required for merely temperaturemaintenance and store up the excess refrigeration for use duringoccasional L. P. G. unloading periods.

One object Y of my invention is to provide a method for the low pressurestorage of liquefied ases. g Another object of my invention is toprovide a method for the low pressure storage of liquefied petroleumgases such as propane.

- Another object of my invention is to provide an apparatus and a methodof operation of this apparatus for the low pressure storage of liquefiedpetroleum gas. y

Yet another object of my invention is to Provide a refrigeration storageunit to operate in conjunction with a refrigeration apparatus for use incooling liquefied petroleum gas during unloading times as well as fornormal cooling of the liquid in storage.

Other objects and advantages of my invention will be apparent from astudy of the following description and drawing which respectivelydescribes and illustrates a preferred embodiment of my invention.

The ligure is in part a. diagrammatic sectional elevation of a preferredform of the apparatus of my invention.

Referring to the drawing, a liquefied petroleum gas storage tank I iscovered with a thick layer of insulation 2. This storage vessel may bevertically disposed, as shown, or may be horizontally arranged ifdesired. The tank has an upper vapor outlet line 3 and a lower drainageline 4. A side outlet line 5 is located in the tank at such a point asto permit withdrawal of liquid from the tank at a point at least somedistance from the bottom. A return line 6 is located at any desiredpoint butA preferably at some distance from the vapor outlet pipe 3.

A brine or other solution tank I2 is also covered with a thick layer ofinsulation. Disposed in the lower portion of this tank is a coil Boneend of which is joined to a line 'I which in turn is joined with pipesSand II, as shown. The other end of the coil 8 connects with a line 9and this line serves as an inlet to a pump I0, while the tank inlet pipe6 serves to convey fluid from the pump into the tank I.

In the upper portion of the brine tank I2 is disposed a coil I4 the endsof which are connected tosome lines I5 and I8 by connecting pipes ortubes I1 and I8, respectively. Line I8 carries a motor valve I9 which isadapted to operate according to the temperature within the tank I2. Athermostat 20 is located in the tank as shown and is adapted through acontroller mechanism 2| to cause the valve I9 to open and to close. Whenthe temperature within the tank I2 rises to above a predetermined valuethe thermostat 20 causes controller 2| to open the valve I9, and thevalve closes when the temperature in the tank drops below apredetermined value.

The storage tank I is also equipped with a series of coils 22 the endsof which are connected to the pipes I5 and I6. In a manner similar tothat given for tank I2, the tank I is equipped with a thermostat 23which is adapted to operate through a controller mechanism 35 to openand to close a valve 24 in line Il.

The lines I and I6 are adapted to carry a refrigerant material, line I6carrying the liquid refrigerant and line I5 being the return line. Acompressor is adapted to compress the gaseous refrigerant while incondenser 26 the compressed refrigerant is cooled and condensed.Connections 21 and 28 carry coolant to and from the condenser 26.

Someanchors 29 are adapted and arranged to ilx the coils 8 and the coilsI4 against movement and to steady them against vibration. In additionthe anchors hold the coils against any buoyant effect occasioned bythepresence of ice in case the tank I2 contains a. water solution.

In the operation of my apparatus the compressor 25 and the cooler orcondenser 26 are operated for a period of time to circulate arefrigerant through lines I6, I8, expansion valve I9. coil I4, andreturn lines I1 and I5. On passage through the expansion valve I9,cooling occurs and this cooling is transferred from coils I4 to water,or a brine solution or other liquid cold storing medium 30. Water may beused for this purpose When it is desired to store the liquefied gas attemperatures about 35 F. or higher. When the heat exchange medium 30 intank I2 has been suillciently cooled then the system is in condition toreceive a car of liquefied gas for storage.

For unloading a car of liquefleld gas, a valve 3| in line I6 just aheadof the expansion valve 24 is opened and refrigerant passed through theeX- pansion valve 24, cooling coil 22 in the storage tank I. The sourceof liquid is connected with the inlet line II, and the inlet valve 32opened, a valve 33 in line 'I is opened and liquefied gas under tank carpressure ilows through the lines II, 1, coils 8, line 9, and throughpump I0 and line 6 into the storage tank I. Pump I0 may be turned on atany desired time.

As liquefied gas from the tank car flows through the coil 8 in thechilling tank I2, the liquid becomes cooled and is passed in thiscondition into the storage tank I. With refrigerant in the storage tankcoil 22 the liqueed gas entering the storage tank I is maintained in acooled condition, Thus with the refrigeration reservoir in a fullychilled condition, I am able to unload a tank car of liquefied petroleumgas in a relatively short time.

After a. car of the liquefied gas has been unloaded into the storagetank I, not much refrigeration is required to keep it in a sufficientlycooled condition. Thus for maintaining the liquefied gas at apredetermined low temperature, it is merely necessary to open a valve 34in line 5, and the valve 33 in line 1, with valve 32 in line II ofcourse closed and by means of pump Ill circulate the liquid from thestorage tank through the cooling coil 8 and back to the storage tank.

As mentioned hereinbefore, to maintain the liquefied gas, once cooled,in the cooled condition requires a relatively small amount ofrefrigeration, and this consideration is the main factor in determiningthe size of refrigeration unit (compressor 25condenser 26) to install. Iuse a compressor 25condenser 26 just slightly larger in capacity thanthat required for temperature maintenance and I operate thisrefrigeration at capacity and in do doing am able to impart sufficientchilling to the solution 30 to cool the liqueed gas circulating in coils8 and to cool the solution 30 to a sufficiently low temperature forcooling liquefied gas during unloading times.,

'I'he capacity of the brine tank I3 is so designed that the liquid 30therein can store up sufficient cooling for tank car unloading purposes.And similarly the size and capacity of the refrigeration unit is soselected that it can maintain the liquefied gas in storage at a desiredtemperature and simultaneously cool the liquid 30 in the brine tank I2so as to have sufficient cooling in storage for tank car unloadingpurposes.

The brine or other solution in the tank I2 may become frozen in part orentirely during the refrigeration storing up period. If water solutionssuch as salt and water, or calcium chloride and water or another saltsolution is used, the water may freeze and if continued for asufdciently long period the entire brine or salt solution may freeze.Under these conditions rather large amounts of refrigeration can bestored and yet be readily available. If such a material as ethyleneglycol or the like is used, and freezing occurs, the frozen mass will beslushy at first and will not harden until after its temperature has beendecreased to quite an appreciable extent. Under this condition then alarge amount of refrigeration is in storage.

Conventional procedure is to use a large size refrigeration' unitcorresponding to 25--26, in fact one which is suiliciently large fortemperature maintenance purposes (in tank I) and at the same time tocool propane being unloaded, It will be obvious to those skilled in theart that without my herein disclosed refrigeration storage anexcessively large amount of refrigeration is required during unloadingtimes in order to unload car of liquid propane in a reasonable length ofime.

Demurrage payments on tank cars is an additional consideration in favorof my refrigeration storage for rapid tank car unloading. Further,overtime labor required for night unloading, runs up costs when mystorage system is not used.

From vapor pressure data of propane it is obvous to those skilled insuch art that by storing at low temperatures, low pressure tanks may beused. At F. propane has a vapor pressure of about 184 pounds per squareinch, at 32 F. its vapor pressure is about 68 pounds per square inch,and at 0 F. its vapor pressure is about 39 pounds. From these gures itwill be obvious that much lighter steel can be used in making thestorage tank I for storing propane under 39 pounds pressure than forstorage under 184 pounds pressure. When installing storage tankssufliciently large to hold from 11/2 to 21/2 tank cars capacity, thecost of such tanks for high pressure storage is excessive.

For the storage liquid 30 in tank I2, I may use water in case storage intank I is desired to be about 35 F. For lower storage temperature a saltwater brine, or a calcium chloride brine, or an ethylene glycol-watermixture may be used. The particular material to be used may be selectedfrom among many available depending upon conditions of a giveninstallation.

The refrigerant to use in the refrigeration circuit may be ammonia, orethane or even propane, or any other material desired. If using propanefrom the storage system for use in the refrigeration circuit provisionwill probably need be made for making certain the propane is dry frommoisture, or of refrigeration grade.

The type of compressor 25 and condenser 28 may be selected from amongthose commercially available. The thermostats 20 and 23, and theirauxiliary apparatus, such as controllers 2l and l5, and motor operatedexpansion valves I8 and 2l may be selected from standard equipment fromequipment supply houses.

The kind and method of application of the insulation 2 and I3 applied totanks I and I2 may be any type desired, as long as it is suitable forthe purpose at hand. The pump I 0 need not be special, but may beobtained commercially from supply houses selling such equipment.

Valves and other auxiliary equipment have not been shown for purposes ofsimplicity but the use of such equipment will be readily understood bythose skilled in the art.

It will be obvious to those skilled in such art that many variations andalterations of my broad idea may be made without departing from theintended spirit and scope of my invention.

Having disclosed my invention. I claim:

1. A liquefied gas storage system comprising a storage tank having anoutlet; a refrigeration reservoir; a first conduit commuicating at oneend with said storage tank circuitously passing through saidrefrigeration reservoir and communicating at its downstream end withsaid storage tank; a pump in said first conduit downstream of saidrefrigeration reservoir; a second conduit circuitously passing throughsaid storage tank and being joined at its .ends by a condenser, saidcondenser being adapted for the passage of coolant therethrough; acompressor in said second conduit upstream of said condenser; a thirdconduit communicating with said second conduit at a point downstream ofsaid condenser, circuitously passing through said refrigerationreservoir and communicating at its downstream end with said secondconduit at a point upstream f said compressor; a valve in said thirdconduit upstream of said reservoir; thermostat means within saidreservoir; control means adapted so as to operate said valve in saidthird conduit in accordance with temperature change in said reservoir; avalve in said second conduit downstream of said condenser; thermostatmeans 'in said storage tank; control means adapted so as to operate saidvalve in said second conduit in accordance with temperature change insaid storage tank; and an inlet conduit communicating with said firstconduit upstream of said reservoir.

2. A liquefied gas storage system-adaptedfor the storage of. saidliquefied gas at a temperature below atmospheric and at acorrespondingly lower pressure, adapted for said lower temperaturestorage during periods of adding liquefied gas to increase the Volume ofliquid in storage, comprising a liquefied gas storage tank;refrigeration reservoir means: first conduit means passing through saidreservoir means to said storage tank; third conduit means for addingliquefied gas to said first conduit means; second conduit meansextending between said storage tank and the inlet end of said firstconduit means; and refrigeration means in direct heat exchange with saidrefrigeration reservoir means and said flrst conduit means.

3. A method for maintaining stored liquefied gas in a cooled conditionin a storage system during periods oi' addition of liquefied gas, atsubstantially atmospheric temperature, to said cooled liquefied gas instorage which comprises passing a refrigerant in indirect heat exchangewith said liquefied gas in storage; passing a portion of saidrefrigerant in indirect heat exchange through a refrigeration reservoirzone; and passing additional liquefied gas in indirect heat exchangethrough said refrigeration reservoir zone into said storage. r

4. The method of claim 3 wherein the liqueed gas is a liquefiedpetroleum gas.

5. A method for maintaining a liquefied gas in a cooled condition in astorage system during and after addition of liquefied gas to said systemwhich comprises passing a refrigerant in a first indirect heat exchangewith said liquefied gas in storage; controlling the flow of saidrefrigerant in said first heat exchange in accordance with temperaturechange within said storage; passing a portion of said refrigerant in asecond indirect heat exchange through a refrigeration reservoir zone;controlling the flow of said refrigerant in said second heat exchange inaccordance with temperature change in said refrigeration reservoir zone;passing additional liquefied gas in indirect heat exchange through saidrefrigeration reservoir zone into said storage; and after said additionof liquefied gas cycling a portion of said liquified gas from storage inindirect heat exchange through said refrigeration reservoir zone andback to said storage.

6. A method for maintaining a liquefied gas in storage in a cooledcondition during periods of.

addition of liquefied gas from a transportation source, at substantiallyatmospheric' temperature, to said cooled liquefied gas in storage,comprising maintaining a first liquefied gas in storage in a cooledcondition by passing a major portion of a stream of refrigerant inindirect heat exchange with said first liquefied gas in storage; passinga minor portion of said stream of refrigerant during an extended periodof time in Indirect heat exchange relation with a refrigeration storagezone, whereby said refrigeration storage zone becomes cooled; passing asecond liquefied' gas from said transporation source in indirect heatexchange relation with said cooled refrigeration storage zone, wherebysaid second liquefied gas becomes' cooled; and passing said cooledsecond liquefled gas into the main body of cooled rst liquefied gas instorage.

7. The method of claim 6 wherein the liquefied gas is a liquefiedpetroleum gas.

AOWEN L. GARRE'rsoN.

REFERENCES CITED The following references areof record in the /f//f//f/Certificate of Correction Patent No. 2,488,813 November 22, 1949 OWEN L.GARRETSON It is hereby certied. that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 3, line 69, for the words in do read fifn, so; column 5, line 61,for direct read lindirect;

and that the said Letters Patent should be read with these correctionstherein that the same may conform to the record of the case m the PatentOflice.

Signed and sealed this 18th day of April, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

